Ceramic multilayer circuits have been used for many years to increase circuit functionality per unit of area. With single layer circuits, all discrete components must be mounted on the surface of the single layer. The number of discrete components and hence, the complexity and size of the circuitry, is limited by the size of the single layer surface. With multilayer circuits, passive components such as capacitors and resistors can be embedded into the alternating dielectric and patterned conductive layers which make up the body of the multilayer circuit. The patterned conductive layers and components within the body of the multilayer circuit are electrically connected by vias which are filled with conductive metallization. In this way, the density and complexity of the circuitry can be increased without significantly increasing the dimensions of the entire construct.
Today, circuits are being used in increasingly varied applications. These new applications make new demands on the circuits. One such application pertains to circuit assemblies comprising active and passive components. In some cases, the active components are housed in plastic leaded chip carriers having a thermal coefficient of expansion (TCE) of 100 which are soldered to metallized ceramic having a TCE of less than 100. This application requires the circuit assemblies to withstand hostile temperature environments, such as thousands of cycles wherein the circuit assemblies are repeatedly placed in an oven maintained at 150.degree. C. for 30 minutes and then transferred to a chamber maintained at -50.degree. C. for another 30 minutes. A major problem encountered by multilayer circuit assemblies under these conditions can be rupture of the solder bond between the active components and the metallized ceramic due to the different TCE's of the plastic leaded chip carriers and the metallized ceramic. This rupture destroys the integrity of the electrical connection between the discrete active components soldered onto the surface of the multilayer body and the patterned conductive layers within the multilayer body. Applicants have discovered a multilayer interconnect which overcomes this problem of the TCE mismatch, offers interconnect design advantages such as a flex/rigid constructions, and is capable of withstanding thousands of thermal cycles in hostile temperature environments such as those encountered in automotive applications, e.g., under the hood, etc.